High speed packaging of articles in a film wrapper has been commonly accomplished by confining the articles within a tubular wrapper which is then cut off and closed by sealing to form the individual packages.
Length of the packages will vary with the length of the articles being wrapped. The sealing and cutoff machine must accommodate packages of various lengths and must produce a reasonable amount of dwell time during sealing so that the sealing can be efficiently accomplished through all of the layers of film that may be present in the seal area. The sealable film material may vary considerably in its characteristics and in some instances, the film material will require a significant dwell time during sealing in order to produce the seal of the type desired. Oftentimes packages will have gussets at the sides which increases the number of thicknesses through which sealing must be accomplished. The film material may be polyethylene, or foil with a polyethylene backing laminated to it, or any of a wide variety of films of a wide variety of thicknesses.
In order to accommodate packages of various lengths, prior art machines have releasably mounted sealing and cutoff heads on a rotor so as to grip, seal, and cut off the tubular film casing between adjacent articles as the head revolves with the rotor. A certain amount of dwell time is thereby obtained during which sealing is accomplished. Because the sealing and cutoff heads are releasably mounted on the rotor, the spacing therebetween is indeterminate. As the entubed articles enter the machine, some type of indicator actuates a sealing head and causes it to firmly attach itself to the rotor so as to travel with the traveling entubed article and effectuate the sealing and cutting. After the sealing has been accomplished in the prior art machines, the sealing head is again released from the rotor, to be stacked up with other similar heads, as to be available when needed again to seal and cut off another package.
Somewhat similar machines have been used wherein the sealing and cutoff heads are releasably connected to roller chains so as to travel a straight course, along one of the runs of the chain, during a sealing and cutoff of the tubular wrapper.
However, in the ordinary course of production, the articles being packaged are usually of a constant size. The size of the articles may change somewhat from one production run to the next one, and in view of the reliability of other machinery for accurately spacing the articles from each other along the tubular film casing, the individual sensing of each article is not entirely necessary. Other prior art machines have effectively produced sealing and cutoff of the tubular casing of sheet material for packages of constant length.